The Douglas mailplanes were a family of 1920s American single-seat mail planes designed and built by the Douglas Aircraft Company. The aircraft were used to run the main routes of the United States Air Mail service until the introduction of three-engined aircraft in 1928.

Photos of the Douglas M-2 Mailplane
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The United States Post Office began air mail service in 1918 mainly using variants of World War I biplanes. In 1925, it placed an order with Douglas for a replacement aircraft based on the Douglas O-2 observation biplane. The company modified an O-2 by covering over the forward cockpit to make a mail compartment and moving the pilot into what had been the Observers cockpit. This version was designated M-1.

When the Contract Air Mail (CAM) routes were introduced the newly formed Western Air Express Company (later Western Airlines) ordered six mailplanes with the designation M-2. (This is the version shown on the cover) It also had the provision to carry a passengerinstead of mail in the front cockpit. Just before Western Air Express introduced the aircraft into service (in April 1926 from Los Angeles to Salt Lake City) the Post Office ordered 50 aircraft designated M-3 for its major route network. The M-3 had only minor differences from the M-2. Douglas then re-designed the M-3 to try and increase or double the payload and the new aircraft was deisgnated the M-4. The M-4 had a new longer span wing and the Post Office converted some of the M-3 order to be built as M-4s. One M-4 was also bought by Western Air Express and this was designated the M-4A. With the introduction of three-engined aircraft types from 1928 the Douglas mailplanes were withdrawn from service, some were sold but most were scrapped.

Jo Kotula revisited this airplane in the "Box Art" for the Aurora kit for the Douglas M-2 Mailplane.